Cleaning operations in public facilities such as restaurants, hotels, food and beverage plants, hospitals, etc. typically use a cleaning product having sanitizing, disinfecting and/or antimicrobial properties. In some cases, cleaning products may interact with certain chemical compounds (e.g., dipicolinic acid) present in some microbial spores to destroy microbes. Alternatively, certain chemical compounds may be added to cleaning products to improve their chemical stability and/or shelf-life. For instance, dipicolinic acid (DPA) can be added to certain cleaning products to improve their resistance to heat, thereby reducing the rate of degradation of the cleaning products when exposed to heat and extending the use of such cleaning products in Dipicolinic acid exhibits fluorescence when excited by electromagnetic radiation of certain wavelengths, the concentration of dipicolinic acid in a solution can be measured by measuring the fluorescence of the solution. The intensity of fluorescence emitted by the solution may depend on the concentration of dipicolinic acid in the solution. For instance, the intensity of fluorescence emitted by the solution may be directly proportion to the concentration of dipicolinic acid. By measuring the intensity of the fluorescence emitted by dipicolinic acid, the concentration of dipicolinic acid can therefore be determined.
Fluorometers for measuring fluorescence of a sample are relatively well known. An exemplary fluorometer for measuring fluorescence is disclosed in U.S. Pat. No. 8,269,193 and U.S. Pat. No. 8,352,207 both assigned to Ecolab Inc., St. Paul, Minn., the disclosure of each of which is here by incorporated by reference in its entirety. Fluorometers generally have a source of electromagnetic radiation that can excite a sample (e.g., dipicolinic acid solution of an unknown concentration), and a detector adapted to measure the intensity of fluorescence emitted by the electromagnetic radiation.
In many situations the concentration of a substance of interest (e.g., dipicolinic acid) in a solution (e.g., cleaning solution) may be very low. For instance, regulatory requirements may necessitate that only a minimum level of the substance of interest (e.g., dipicolinic acid) is present in a target area (e.g., a healthcare facility, food and beverage production and packaging facility). In such cases, the intensity of fluorescence emitted by such substances of interest can be proportional to their concentration. Low concentrations (e.g., on the order of a few hundred parts per billion) may result in decrease in intensity of emitted fluorescence. For instance, the fluorescence may decrease directly proportional to the decrease in concentration (or by diluting the substance of interest). Typical fluorometers known in the art may not be able to measure such low levels of fluorescence with high accuracy and sensitivity.